The present invention relates to processes and apparatus for recovering and purifying epichlorohydrins from a mixture comprising the same such as the effluent generated by a process for dehydrochlorination of dichlorohydrins.
Epichlorohydrin is a widely used precursor to epoxy resins. Epichlorohydrin is a monomer which is commonly used for the alkylation of para-bisphenol A. The resultant diepoxide, either as a free monomer or oligomeric diepoxide, may be advanced to high molecular weight resins which are used for example in electrical laminates, can coatings, automotive topcoats and clearcoats. Processes and apparatus for making and purifying epichlorohydrin are known in the state of the art.
British Patent Specification 974,164, for example, discloses a process and apparatus for the production of epichlorohydrin from dichlorohydrin in which an aqueous reaction medium comprising an inorganic alkali hydroxide, water and dichlorohydrin are mixed and then treated with steam in a reactor column at a temperature below 55° C. to strip epichlorohydrin formed by the reaction between the inorganic alkali hydroxide and dichlorohydrin from the reaction mixture as a gaseous water-epichlorohydrin azeotrope. The overhead is condensed and separated in a liquid-liquid phase separator into an aqueous phase, which is recycled to the dehydrochlorination reactor column, and an organic phase, which is fed to a drying column to remove epichlorohydrin and residual water as a vapor phase. The vapor phase is condensed and recycled to the liquid-liquid phase separator to remove residual water from the drying column.
The bottoms from the drying column are fed to a finishing column. The vapor phase from the finishing column is condensed to recover epichlorohydrin. The liquid phase effluent from the bottom of finishing column is mixed with water to extract residual unreacted dichlorohydrin for recycle to the dehydrochlorination process.
While that process is capable of producing epichlorohydrin, further improvements in epichlorohydrin yield and purity and lower energy and capital investment requirements for a given production rate and purity are desired. Opportunities remain to further improve the recovery of epichlorohydrins in a form that can be used in subsequent conversions, such as the conversion to epoxy resins.
Accordingly, it is desired to provide improved processes and apparatus for separating the product epichlorohydrin from the dehydrochlorination reaction effluent. These and other problems are solved by the present invention described below.